1. Field of the Invention
The present invention relates to an apparatus and method for a Transmit/Receive Antenna Switch (TRAS) in a Time Division Duplex (TDD) wireless communication system. More particularly, the present invention relates to an apparatus and method for protecting a Low Noise Amplifier (LNA) from a Radio Frequency (RF) transmit signal.
2. Description of the Related Art
In general, a Transmit/Receive Antenna Switch (TRAS) performs a function of switching between a high power Radio Frequency (RF) transmit signal and a low power RF receive signal in a Time Division Duplex (TDD) wireless communication system. A TDD system divides the same frequency in time and uses the divided frequencies for transmission and reception. In a transmission mode, the TRAS blocks the introduction of a transmit power into a Low Noise Amplifier (LNA) of a receiving end, thus protecting the LNA. In a reception mode, the TRAS reduces an amount of noise introduced from a transmit end, thus preventing a reduction in sensitivity when receiving a signal.
FIG. 1 is a block diagram illustrating a construction of a TDD wireless communication system using a TRAS according to the conventional art.
Referring to FIG. 1, a TDD controller 100 divides a transmission/reception frame by units of time and outputs a control signal for controlling an operation of a transmission/reception mode depending on the divided time. The control signal is output to a transmitter 102, a receiver 106, and a TRAS 110. A Power Amplifier (PA) 104 amplifies a transmit signal from the transmitter 102 and outputs the amplified signal to the TRAS 110. An LNA 108 low-noise amplifies a receive signal from the TRAS 110 and outputs the amplified signal to the receiver 106.
The TRAS 110 switches between a transmission path and a reception path depending on a control signal from the TDD controller 100 and performs an operation corresponding to a transmission mode or reception mode, respectively. That is, when receiving a control signal indicating a transmission mode operation from the TDD controller 100, the TRAS 110 connects a transmission path from the PA 104 to an antenna 114, thus outputting a transmit signal received from the PA 104 to a Front End Block (FEB) 112. At this time, the TRAS 110 prevents the introduction of the high power transmit signal into the LNA 108. When receiving a control signal indicating a reception mode operation from the TDD controller 100, the TRAS 110 connects a reception path from the antenna 114 to the LNA 108, thus outputting a signal received from the FEB 112 to the LNA 108. At this time, the TRAS 110 reduces an amount of noise received from the PA 104.
In the transmission mode of the TDD wireless communication system, an insertion loss of the transmission path ranging from the PA 104 to the antenna 114 may have influence on a capacity of the PA 104. To reduce this loss, the TRAS 110 has to be designed and constructed to minimize the insertion loss of the transmission path and isolate the LNA 108 of a receiving end from the transmission path. In the reception mode, an insertion loss of the reception path ranging from the antenna 114 to the LNA 108 and a noise degree of an input signal of the LNA 108 have influence on reception performance. Thus, the TRAS 110 has to be designed and constructed to minimize the insertion loss of the reception path and isolate an output end of the PA 104 from the reception path.
By realizing a function of a TRAS using an RF switch 205 of FIG. 2 or using a circulator 334 and a reflector 338 of FIG. 3, a conventional TDD wireless communication system isolates transmission/reception paths and protects an LNA of a receiving end.
A conventional method using a Single Pole Double Throw (SPDT) RF switch 205 is described below with reference to FIG. 2.
Referring to FIG. 2, in a transmission mode, the SPDT RF switch 205 is switched to forward a transmit signal from a transmitter 201 to an antenna feed line and, in a reception mode, is switched to forward a receive signal from the antenna feed line to a receiver 203. That is, the RF switch 205 switches transmission/reception paths by a TDD control signal. However, the electrical RF switch used in the above method has the disadvantages of being expensive and being difficult to implement.
A conventional method using a circulator 334 and a reflector 338 is briefly described below with reference to FIG. 3.
Referring to FIG. 3, according to directionality shown in a TRAS 330, the circulator 334 forwards a signal from a transmitter 310, a PA 312 and an isolator 332 to an FEB 350 and an antenna 352 and forwards a signal from the FEB 350 to the reflector 338 and potentially to an LNA 322 and a Receiver 320.
A first controller 336 turns ON/OFF a reflection operation of the reflector 338 depending on a transmission/reception mode indicated by a control signal from a TDD controller 300. If the reflection operation of the reflector 338 turns ON, a signal output from the circulator 334 is totally reflected by the reflector 338 and is terminated by the isolator 332. If the reflection operation of the reflector 338 turns OFF, a signal output from the circulator 334 is forwarded to a high frequency switch 342 by the reflector 338.
A second controller 340 turns ON/OFF a switching operation of the high frequency switch 342 depending on a transmission/reception mode indicated by a control signal of the TDD controller 300. If the high frequency switch 342 is switched OFF, a signal from the reflector 338 is not forwarded to the LNA 322. If the high frequency switch 342 is switched ON, a signal from the reflector 338 is forwarded to the LNA 322 and then to the Receiver 320.
By providing isolation of a high frequency signal between the transmission/reception paths as above, the method using the circulator and the reflection block can prevent the introduction of a high frequency transmit signal into the LNA, and has an advantage of size and cost aspects compared to the method using the RF switch.
However, the method using the circulator and reflection block has a problem in that, if a failure of power supply to the TRAS occurs, it is not possible to isolate the transmission/reception paths and thus it is not possible to protect the LNA from the high frequency transmit signal. If it is intended to protect the LNA even when a failure of power supply occurs, the method requires a complex structure to control several blocks depending on a state of the TRAS.
Accordingly, there is a need for an improved apparatus and method for a Transmit/Receive Antenna Switch (TRAS) in a Time Division Duplex (TDD) wireless communication system.